Stereomicroscope

ABSTRACT

A stereomicroscope of the telescope type includes a first beam path and a second beam path, wherein in the first beam path a first telescope system and in the second beam path a second telescope system are provided, wherein the magnifications of both telescope systems are equal and can be changed synchronously to each other, and wherein a common main objective is allocated to both beam paths. In order to increase the resolution without loss in depth of field, it is proposed that at least one optical element of the first telescope system has, compared to at least one corresponding optical element of the second telescope system, a different optically effective diameter.

Priority is claimed to German Patent Application No. DE 10 2005 040472.3, filed Aug. 26, 2005, and to German Patent Application No. DE 102006 036 300.0, filed on Aug. 3, 2006, both of which are incorporated byreference herein.

The present invention relates to a stereomicroscope. Thestereomicroscope can be designed according to Greenough with, in eachcase, one objective per stereo channel, or as a telescope type with amain objective common for both stereo channels. The stereomicroscope isdetachably connected to a focusing arm or incorporated therein.

BACKGROUND

Stereomicroscopes are used to manipulate objects under visualobservation and/or to make fine object details visible. The objectmanipulation preferably takes place under low magnification and requiresgood 3D reproduction. For detail recognition, rapid switching to highmagnifications with high resolution is desired without change ofinstrument.

Stereomicroscopes provide two views of the object at various observationangles which are perceived by the viewer as a three dimensional image ofthe object. If the angle between the two observation directions isunusually large, the object appears spatially distorted.

Numerous descriptions of the telescope type of stereomicroscopes appearin the literature: see “Optical Designs for Stereomicroscopes”, K-P.Zimmer, in International Optical Design Conference 1998, Proceedings ofSPIE, Vol. 3482, pages 690-697 (1998). The U.S. Pat. No. 6,816,321discloses an afocal zoom system for high performance stereomicroscopeswith which zoom factors z (ratio of maximum to minimum zoommagnification) of more than 15 can be achieved.

Stereomicroscopes with such a design include—apart from optional bolt-onmodules—a main objective, which images the object at infinity, twodownstream parallel telescopes for varying the magnification and twoobservation units (binocular tubes) comprising a tube lens, invertingsystem and eyepiece for visual observation with both eyes. Thetelescopes can be designed as Galilean telescopes for step-by-stepmagnification selection or as afocal zoom systems for continuousmagnification selection. According to the prior art, two identicaltelescopes are arranged symmetrically to a plane of symmetry of thedevice, wherein the plane of symmetry divides the object symmetricallyinto a right and a left half. The distance between the telescope axes isreferred to as the stereo basis. The numerical aperture of thismicroscope is given by the semi-diameter of the entrance pupil of thetelescope or spy glass divided by the focal length of the mainobjective.

The numerical aperture of a microscope of this type is therefore limitedin the prior art. In order to increase the numerical aperture it isknown to expand the entrance pupil diameters of the telescopes which,because of the arrangement of the two telescopes next to each other,results in an expansion in the stereo basis and therefore in thedrawback of large equipment dimensions, or to shorten the focal lengthof the main objective, thereby disadvantageously reducing the workingdistance and increasing the power required of the main objectiveexcessively. In both cases the angle between the directions ofobservation is expanded, resulting in, or increasing, spatialdistortion.

U.S. Pat. No. 5,603,687 describes an asymmetrical stereooptic endoscope,in which two objective systems with different diameters of the entrancepupils are arranged parallel next to each other. Both objectives produceimages of the object on a sensor surface via light conductors or lightfibers. From these CCD sensors for example, the image data aretransmitted after digital processing to a monitor, that is to say theycan be spacially perceived for example with a stereomonitor. It isstated that despite varying diameters of the two endoscopic channels theviewer perceives a stereoscopic image with a resolution and abrightness, as they result from the channel of larger diameter. Thesecond channel of smaller diameter primarily serves to produce astereoscopic vision or impression.

The conditions in the case of a stereomicroscope of the telescope typeof the design as described above are in principle different than in thecase of an endoscope in accordance with U.S. Pat. No. 5,603,687.Firstly, the viewing of the object takes place as a rule (at least also)directly with the eyes, without prior digital processing. Such digitalprocessing will or can be used, if additionally documentation is to bemade via connected cameras. It is not clear from the US documentmentioned, how in the case of the embodiment described therein an objectcan be viewed directly visually. Furthermore, the projection onto asensor surface (fixed focus) limits the depth of field of the displaysince the accommodation capacity of the eyes is out of action.

The magnification of an endoscope depends on the object distance. Athigh magnifications the object distance is normally minimal. In thiscase the overlap range of the fields of view of the two objectives beingarranged next to one another is minimal. Therefore, stereoscopicviewing, which is only possible in the overlap range, is reduced in thiscase. At low magnifications however the overlap is large, but thenumeric aperture is small, which results in high depth of field. Henceit follows that the image definition or quality of 3D objects onlyreduces slowly with the distance to the focus plane. This circumstancefavours the merging of the two fields into a spatial image, inparticular if the object depth is less than the depth of field.

A main component of a stereomicroscope of the type described is thetelescope systems (discrete magnification changer or continuous zoom) inthe two stereo channels. Telescope systems are not common in endoscopy.In the US document mentioned, therefore, a variation of the displayscale or reproduction scale is not discussed.

For stereoscopic viewing the depth of field is important. In contrast tothe stereoendoscope described above high power stereomicroscopes of thetelescope type advantageously use the accommodation capacity of theeyes. A magnification variation takes place without changing thefocusing of the equipment. There is no difference in the object clipbetween the right and the left field over the whole magnification range.The numeric aperture and thus the resolution of the stereomicroscope areadapted to the magnification and prevent empty magnifications. At highmagnifications the depth of field is very small, in many cases smallerthan the object depth in such arrangements. The image quality of 3Dobjects therefore considerably decreases with the distance to the focusplane. Thus, it cannot be assumed that the merging of the fields to aspatial image observed with a stereoendoscope under typically lowmagnification and high depth of field can be transferred to theconditions, which exist with a high power microscope in particular athigh magnifications, if the stereoscopic channels due to differentapertures produce images of different resolution and depth of field.

A further, not to be neglected, criterion is that of the imagebrightness, which is different in the case of the US document mentioned,due to the different entrance pupil diameters of the endoscopicchannels. Here the digital processing of images has the advantage thatboth fields can be shown equally brightly on the monitor aftercorresponding correction. Such corrections are not possible in the caseof direct visual viewing, as is the case with stereomicroscopes.

Furthermore, it would be detrimental with an arrangement discussedabove, if the higher power of one of the stereoscopic channels could notbe used by a user having eyes of different capability, if thestereoscopic channel of higher power was assigned to the eye of lowercapability.

U.S. Pat. No. 3,655,259 describes a somatic microscope, which is to beused as an endoscope. This microscope has been developed as astereomicroscope from the Greenough type. The two stereo channels arearranged at a given opening angle to one another and in each casepossess their own objectives, which are designed here as mini lenses,rod lenses or as final sections of a glass fibre. The underlying problemwith this somatic microscope of this document is due to the fact thatwith the use of two objectives these cannot be placed arbitrarily closeto each other, since a lens combination is selected as the objective andthe use of a single objective lens is not possible due to increasingspherical aberrations, in particular if high magnification is required.The object of the document mentioned is therefore to find an arrangementwhich permits minimum endoscope diameter at high magnification.

U.S. Pat. No. 4,862,873 describes a further stereoendoscope whichcomprises two channels arranged parallel to each other, wherein one ofthe channels is to be used for lighting and the other is to be used forobservation respectively. In order to produce a stereoscopic imageimpression the two channels are switched over by a motorized prism 30times per second for example.

German Patent DE 102 25 192 B4 describes an arrangement for an objectivefor stereomicroscopes of the telescope type as well as a correspondingstereomicroscope. The design, functional mode as well as theinterrelationships of magnification, resolution power and vignetting,thereof are incorporated herein by reference.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a stereomicroscope withimproved detail recognition compared with conventionally designedstereomicroscopes, without this leading to an increase in theconstruction volume of a stereomicroscope or to limitations in theusability of the conventional working range of a stereomicroscope. Afurther or alternate object of the present invention is improving thedetail recognition without detrimentally reducing the depth of field.

The present invention provides a stereomicroscope of the telescope typecomprising a first beam path and a second beam path, wherein in thefirst beam path a first telescope system and in the second beam path asecond telescope system are provided, wherein the magnifications of bothtelescope systems are equal and can be changed synchronously to eachother and wherein a common main objective is allocated to both beampaths, characterised in that at least one optical element of the firsttelescope system compared with at least one corresponding opticalelement of the second telescope system has a different opticallyeffective diameter.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention are described below and shownschematically in the drawings, in which:

FIG. 1 shows a perspective view of a stereomicroscope;

FIG. 2 shows a schematic diagram of the optical design of astereomicroscope of the telescope type according to the prior art;

FIG. 3 shows the progression of the numerical aperture nA for a typicalhigh power stereomicroscope as a function of the magnification;

FIG. 4 shows the progression of the depth of field T for the high powerstereomicroscope described above as a function of the magnification;

FIG. 5 illustrates schematically the optical design of a firstembodiment of the invention;

FIG. 6 shows the progression of the numerical aperture nA as a functionof the magnification;

FIG. 7 shows the progression of the depth of field T as a function ofthe magnification;

FIG. 8 a shows a first setting possibility of the positioning of themain objective in relation to the magnification changer (“symmetricalarrangement”;

FIG. 8 b shows the positioning of the main objective in such a way thatthe optical axis of the main objective is closer to the optical axis ofthe telescope system of the greater diameter of the entrance pupil(“asymmetrical arrangement”;

FIG. 8 c shows the special case in which the optical axis of the mainobjective and the optical axis of the telescope system coincide with thelarger entrance pupil diameter (“centric arrangement”;

FIG. 9 shows the beam path of the first telescope system at maximummagnification; and

FIG. 10 shows the beam path of the first telescope system at minimummagnification.

DETAILED DESCRIPTION

It is advantageous for the stereomicroscopes according to the inventionon the one hand to have at low magnifications as a result of a lownumerical aperture a large depth of field and to allow a good3-dimensional reproduction and on the other to have at highmagnifications a high aperture and thus to offer high resolution withoutgenerating empty magnifications, that is to say rising magnificationswithout increasing resolution.

Surprisingly it has been shown that despite the different resolution anddepth of field due to the different optically effective diameters of thetwo stereoscopic channels or beam paths the visual image impression isnot impaired even at high magnifications.

With one embodiment, in which the optically effective diameters of bothstereoscopic channels are different for all magnifications, on the onehand the higher depth of field of the smaller of the two channels and onthe other hand the higher resolution of the larger of the two channelsare always perceived. As the result of expansion of the opticallyeffective diameter of the one channel in relation to the prior art anincrease in the resolution and thus in the detail recognition without adisadvantage as regards the depth of field can be achieved. Thisadvantage is particularly useful for setting high magnifications.

With another embodiment, in which the optically effective diameters ofthe smaller stereoscopic channel are limited for example by a lensdiameter, both stereoscopic channels can be implemented in a widemagnification range of low magnifications with the same effectivediameter, for which reason the stereomicroscope in this setting worksjust like a conventional microscope. Only at high magnifications, whenthe diameter of the entrance pupil of the larger channel exceeds thediameter of the limiting lens mentioned of the smaller channel, theapertures become asymmetric and the effects described above arerealized.

Furthermore, it is pointed out that the differences in the imagebrightnesses of the two channels, as generally known, correspond to theratio of the surfaces of the entrance pupils. In the first embodimentmentioned above the brightness differences are constant throughout theentire magnification range, in the second above exemplary embodimentbrightness differences only occur at high magnifications.

Also, the resulting brightness differences do not lead to visualimpairment over the entire working range of the stereomicroscope. Thus,the advantages of different channel diameters with the stereomicroscopeaccording to the invention can be used as a function of themagnification, without the disadvantages of these different channelwidths impairing the direct visual viewing of the image. Such a reactionwas not automatically to be expected.

A stereomicroscope according to the invention comprises a first beampath and a second beam path, wherein in the first beam path a firsttelescope system and in the second beam path a second telescope systemare arranged, wherein the magnifications of both telescope systems areequal and can be changed synchronously to each other, and wherein acommon main objective is allocated to both beam paths. At least oneoptical element of the first telescope system has, compared with atleast one corresponding optical element of the second telescope system,a different optically effective diameter.

The optical elements of the first telescope system or the secondtelescope system are lens elements or diaphragms. For at least onemagnification setting or one zoom or magnification range—preferably athigh magnifications—for the same magnification of the telescope systemthe diameter of an entrance pupil of the first telescope system is morethan 10%, in particular 10% to 50%, larger than the diameter of theentrance pupil of the second telescope system.

The first telescope system has formed an optical axis and the secondtelescope system has formed an optical axis parallel to this, whereinthe distance between the optical axes of the telescope systems resultsin a stereo basis. It is advantageous if the diameter of the entrancepupil of the telescope system with the larger optically effectivediameter is larger than the stereo basis. This permits a compactstructure despite different diameters of the stereoscopic channels.

It has been shown that different arrangements of the main objective inrelation to the two telescope systems of a stereomicroscope according tothe invention are possible and expedient.

A first embodiment of the main objective is to be called a “symmetricalarrangement” below. With this embodiment the distances of the opticalaxis of the main objective to the two optical axes of the telescopesystems are equal. This embodiment is described in more detail furtherbelow in connection with the exemplary embodiment in FIG. 8 a. It isseen as an advantage that an object, which is placed centrically to themain objective, is viewed through both stereoscopic channels at the sameopposite angle, whereby the impression of a perpendicular view fromabove arises. However, the relatively large diameter of the mainobjective, which principally causes higher costs for an objectiveoptically corrected accordingly, has a disadvantageous effect.

An alternative embodiment is the “asymmetrical arrangement”, in whichthe distances of the optical axis of the main objective to the opticalaxes of the two telescope systems are of various lengths. Here thedistance of the optical axis of the main objective to the optical axisof the telescope system with the larger optically effective diameter issmaller than the distance to the optical axis of the other telescopesystem. This embodiment will be discussed in more detail further belowin connection with the exemplary embodiment in FIG. 8 b. With thisembodiment the diameter of the main objective can (only) be selected aslarge as the sum of the diameters of the two stereoscopic channels.This, in comparison with the symmetrical arrangement, leads to a mainobjective of smaller diameter with the lower costs and higher opticalquality associated therewith. The only disadvantage, in practice oflittle significance is the fact that an object, placed centrically tothe main objective, for example a needle, appears as though viewedslightly from the side.

A further embodiment, which is described in more detail further below inconnection with the exemplary embodiment in FIG. 8 c, is a “centricarrangement”, in which the optical axis of the main objective coincideswith the optical axis of the telescope system with the larger opticallyeffective diameter. This embodiment is selected if stereoscopic viewingis not required, in particular, if images of high magnification and highresolution are to be sent to a documentation interface for example. Inthis connection it has proven advantageous to displaceably arrange themain objective laterally relative to the telescope systems (thusperpendicularly to its optical axis) in order to be able to easilychange over between different arrangements. In practice it has provenexpedient to laterally displace the telescope systems with the tube inrelation to the stationary main objective in order to prevent a shiftingor displacement of the object. Only for the sake of simplicity shouldmention be made of “lateral displaceability of the main objective”.

Lateral displaceability of the main objective is expedient concerningthe different arrangements mentioned at least in the direction of thestereo basis. However, lateral displaceability can also be advantageousin a different direction (thus not only in the direction of the stereobasis, but for example in a direction perpendicular to this) inparticular if the lighting channel used for illumination does notcoincide with the two viewing channels (that is to say the first andsecond beam path). EP 1 010 030 (WO 99/13370) discloses a stereofluorescence microscope, which additionally to the two stereoscopicchannels in the magnification changer comprises a third channel outsidethe stereo basis, which serves to illuminate the object from above. Asto be inferred there from FIG. 2 b a lateral displacement of the mainobjective perpendicular to the stereo basis is advantageous, in order toencompass with a small objective diameter all three channels of thestereo fluorescence microscope mentioned.

Further advantageous embodiments of the invention can be found in theclaims and the following exemplary embodiments.

FIG. 1 is a perspective view of a stereomicroscope 60 according to theprior art. The stereomicroscope 60 comprises a base 71, to which afocusing column 72 is secured. A focusing arm 73 is attached in adisplaceable manner to the focusing column 72, which can be displacedvia adjustment element 74 along the double arrow A-A. Thestereomicroscope 60 has a binocular tube 65 and a zoom system (see FIG.2). The zoom system can be adjusted with adjusting elements 78.

FIG. 2 is a schematic diagram of the optical design of astereomicroscope of the telescope type according to the prior art (seeDE 102 25 192 B4). The object plane 1 is in the front focal plane of themain objective 2. The object 1 a to be investigated or observed is alsolocated in the object plane. In the object plane 1 the object centre 1 bis marked by the vertical line 11. The optical axis 11 a of theobjective 2 coincides with the vertical line 11. In the following theembodiment of the design of the optical system will be described in thedirection of a user. The user detects the image of the object 1 a withhis eyes 52R and 52L. The main objective 2 has a first and secondtelescope system 3R and 3L downstream, which are identical in design.The first and second telescope systems 3R and 3L are arrangedsymmetrically to the vertical line 11 or to the optical axis 11 a. Thetelescope systems 3R and 3L are shown as afocal zoom systems. Thesesystems are, for example, described in U.S. Pat. No. 6,816,321 mentioned(corresponds to DE 102 22 041 B4).

In the zoom systems diaphragms or iris diaphragms 31R and 31L arearranged. The diameters of the iris diaphragms 31R and 31L areadjustable and are set the same way on both sides. These limit thediameters 32R and 32L of the entrance pupils, which are of variable sizeaccording to the zoom setting and diaphragm selection but are the sameon both sides.

The first and second telescope systems 3R and 3L define a first and asecond optical axis 33R and 33L respectively. The distance between theoptical axes 33R and 33L is referred to as the stereo basis b. On thefirst and second optical axes 33R and 33L the telescope systems 3R and3L are subordinate to the first and second observation units 4R and 4L,which are each arranged symmetrically to the vertical line 11. The firstand second observation units 4R and 4L comprise identically designedtube lenses 41R and 41L, which generate the intermediate images 42R and42L, symmetrical inverter systems 43R and 43L for image erecting andeyepieces 51R and 51L. The user detects the image of the object directlywith his eyes 52R and 52L. Optionally in a known fashion further modulescan be introduced into the beam path, such as attachment lenses,filters, polarisers, reflected illumination units, beam splittingsystems for light coupling and decoupling, and so on.

The display by a microscope of this kind is shown by a schematicrepresentation of the marginal beams 61R and 61L of a beam path, whichin the example originates from the object centre 1 b. The marginal beams61R and 61L identify the two illuminating pencils 62R and 62L used bythe microscope. As shown on FIG. 2, the respective illuminating pencils62R and 62L are limited by the diameters 32R and 32L of the entrancepupils, which for their part are determined by the iris diaphragms 31Rand 31L. Since the object 1 a is arranged in the front focal plane ofthe objective 2, the marginal beams run parallel between the objective 2and the zoom. Therefore it is possible in a simple manner to determinethe diameters 32R and 32L of the entrance pupils. The marginal beamsleave the zoom parallel again. Therefore the space behind the zoom isadvantageous for optional accessories. The tube lenses 41R and 41L eachfocus the pencil of rays on a point 42 aR and 42 aL in the plane of theintermediate images 42R and 42L, respectively. The points 42 aR and 42aL are located in the front focal plane of the eyepiece 51R or 51L andis imaged by this at infinity, so that it can be observed with the eyes52R and 52L. Further, it can be seen from FIG. 2 that the angles wR andwL at which the observer perceives the object 1 a with the right or lefteye 52R, 52L, are the same.

As stated in U.S. Pat. No. 6,816,321 (“Afocal Zoom for Use inMicroscopes”) and in DE-102 25 192 B4 (“Objective for stereomicroscopesof the telescope type”) the resolution of the microscope is givenapproximately by:Resolution=3000*nA[Lp/mm],  Equation (1)

where LP/mm stands for line pairs per millimeter and nA is the numericalaperture which in the present case is given bynA=EP/(2*focal length of the objective 2)  Equation (2)

where EP is the diameter of the entrance pupil of the telescope system.

Finally the depth of field T is again of significance. A practical ratiois given by:T[mm]=λ/(2*nA²)+0.34 mm/(Vtot*nA)  Equation (3)

where λ=light wavelength of approx. 550 E-6 mm and Vtot=microscopemagnification including eyepiece magnification.

FIG. 3 shows the course of the numerical aperture nA for a typical highpower stereomicroscope as a function of the magnification. Themagnification is plotted along the abscissa 40. The numerical aperturenA is plotted along the ordinate 44. In this example a focal length ofthe main objective f_(O)′=80 mm, a tube focal length f′_(T)=160 mm, astereo basis b=24 mm and an eyepiece magnification=10× are selected. Theunbroken line 45 corresponds to the full diaphragm opening and thebroken line 46 results if the diaphragm surface is reduced by 40%.

FIG. 4 shows the course of the depth of field T for the high powerstereomicroscope described above as a function of the magnification. Themagnification is plotted on the abscissa 68. The depth of field T isplotted on the ordinate 54. The unbroken line 67 corresponds to the fulldiaphragm opening and the broken line 66 results when the diaphragmdiameter is reduced as stated above. It can be seen from FIG. 4 that byreducing the diaphragm diameter the user can increase the depth offield, but the diaphragm causes a reduction in the numerical aperture nA(FIG. 3) and as a result of equation (1) a loss of resolution.

FIG. 5 is a schematic representation of a first embodiment of thestereomicroscope 60 of the invention. The main objective, the stereobasis and the observation units are unchanged. Optical elements, whichare identical to elements from FIG. 2, are denoted by the samereferences. The maximum magnification setting of the telescope system isshown. It can be seen that the diameter of the right beam path 60R isgreater than that of the left 60L, in this example greater than thestereo basis b.

The invention concerns stereomicroscopes of the telescope type withtelescope systems which—as already stated—can be designed as a stepchanger or zoom system. The two telescopes or telescope systems 3R and3L are according to the invention no longer built symmetrically but aredifferent, in particular, however, having at least different maximumdiameters of the first entrance pupil 32R and the second entrance pupil32L. Advantageously, the maximum diameter of the entrance pupil 32R or32L of one telescope system 3R or 3L is 10-50% larger than that of theother telescope system 3L or 3R. The invention is particularly effectiveif the larger of the two diameters of the entrance pupils 32R or 32L islarger than the stereo basis b, which is possible if the diameter of theentrance pupil 32R or 32L of the other telescope system 3R or 3L issmaller than the stereo basis b.

The magnification changers or the zoom systems of the two telescopesystems 3R and 3L, as explained below, can be designed in such a waythat in the wide range of smaller microscope magnifications thediameters of the entrance pupils 32R and 32L of the two telescopesystems 3R or 3L are virtually identical, but for high magnificationsare different. By means of the unequal entrance pupil diameters theresolution can be increased without the disadvantages described above.

In the case according to the invention of the unequal diameters of theentrance pupils 32R and 32L the user receives two partial images ofdiffering brightness, differing resolution and differing depth of field.Unexpectedly, it has been shown that a difference in brightness of up to50% and the differences in the detail recognition do not adverselyaffect the visual perception and merging of the two partial images intoa 3-dimensional image. On the contrary, surprisingly the object isperceived 3-dimensionally not only with the improved resolutionresulting from the higher numerical aperture but also with the greaterdepth of field resulting from the lower aperture. The invention is basedon the utilisation of this physiological phenomenon for the design ofstereomicroscopes.

While in the first beam path 60R the pencil diameter is determined bythe diameter of the iris diaphragm 31R, limitation of the second beampath 60L is by means of the diameter of the lens component 35L betweenobjective 2 and diaphragm 31L. The objective 2 has a first and a secondtelescope system 3R and 3L which do not have the same design downstreamof it. The optical elements 35R, 31R of the first telescope system 3Rhave a different diameter from the optical elements 35L, 31L of thesecond telescope system 3L. The telescope systems 3R and 3L are shown asafocal zoom systems.

The embodiment of the telescope systems 3R and 3L (right and left) maycomprise different component parts. Here it should be noted that in theoperated condition the rule of equal magnification always applies, thatis to say the magnification of the two telescope systems is changed inunison.

A further possibility for the design of the first and second telescopesystems 3R and 3L is for the first and second telescope systems 3R and3L (right and left) to be designed with a “same construction”, wherein,however, the optically effective diameter of at least one of the opticalelements or a lens component of one of the two telescope systems isdifferent to that at least of one of the optical elements or of a lensmember of the other telescope system The term “optically effectivediameter” means the diameter which describes the pencil of rayscontributing to the image generation when they hit an optical element35R, 35L and penetrate the optical element. With the “same construction”of the telescope systems in the case of an exemplary structure of a zoomsystem in accordance with Table 1 below, apart from the first lens group(surface numbers 101 to 105) the same parts are used for the remainingthree groups on the right and on the left. This is economicallyexpedient because of the possible higher production numbers. Also, forthe first group, all manufacturing parameters are the same except forthe diameter (see Table 1).

The first and the second telescope system 3R and 3L are preferablydesigned as afocal zoom systems, in particular such according to DE 10222 041 B4 for a continuous magnification selection. As regards thestructure and the function mode of such zoom systems express referenceis made to the document mentioned, DE 102 22 041 B4—in order avoidrepetitions.

The design of the first and the second telescope systems 3R and 3L(right and left) each with a diaphragm or iris diaphragm 31L, 31R isillustrated. Here the first diaphragm 31R in the first telescope system3R can be operated independently of the second diaphragm, 31L in thesecond telescope system 3L. Telescope systems without any diaphragm canalso be used.

In a further embodiment of the diaphragm setting the operation of thediaphragms 31R, 31L is set in such a way that in a first setting theratio of the diaphragm openings between the first telescope system 3Rand the second telescope system 3L is set. In a second setting bothdiaphragm openings (with the ratio unchanged) are varied simultaneously.

Similarly through the introduction of a light filter (for exampleneutral density stage or graduated filter) in the beam path with thelarger diameter of the entrance pupils the differences in brightnessresulting from the diameter differences can be reduced or eliminated.Here the filter 37 is advantageously arranged in any of: between themain objective 2 and the telescope system 3, in the telescope system, orbetween the telescope system and the eyepiece as shown in FIG. 5. Thefilter 37 can be operated manually and introduced into the beam pathalong the double arrow 37 a illustrated in FIG. 5. It is likewisepossible for the filter 37 to be varied in its position and thus itsfilter properties by an operation controlled by the magnificationselection. The filter does not adversely affect the resolution or thedepth of field.

In a further embodiment the stereomicroscope is provided with adocumentation port 55. By arranging a beam splitter 56 or a decouplingdevice in the first beam path 60R with the larger diameter 32R of theentrance pupil, the decoupling is achieved. Thus, the high resolution ofthe documentation device 57 is made present. The documentation device 57is a conventional CCD camera or a conventional sensor surface.

Further, the first and/or the second telescope system 3R, 3L can bedesigned to swivel about its longitudinal axis, so that the beam pathwith the larger diameter of the entrance pupils 32R can optionally besupplied to the right or the left eye 52R or 52L of the user.

The invention has a particular advantage in high powerstereomicroscopes, wherein high magnifications and thus also highresolutions are required, in order to prevent a so-called emptymagnification (increase of the magnification with constant resolution,that is to say, without increase in the detail recognition). Themagnification ratio Vmax/Vmin should be greater than 10 instereomicroscopes. Zoom systems with a zoom factor z>10 are normal forthis purpose. From the ratios described the invention is particularlyeffective.

FIGS. 6 and 7 show the course of the numerical aperture nA and the depthof field T for an embodiment with maximum diameter EP=27 mm on the rightside and maximum diameter EP=21 mm on the left side. Again a focallength of the main objective of f_(O)′=80 mm, a tube focal lengthf′_(T)=160 mm, a stereo basis b=24 mm and an eyepiece magnification of10× are selected. The unbroken line 75 on FIG. 6 arises for the beampath with the large diameter 32R, and the broken line 76 for the beampath with the smaller diameter 32L. The unbroken line 85 in FIG. 7arises from for the beam path with the large diameter 32R, and thebroken line 86 for the beam path with the smaller diameter 32L. It canbe seen from FIG. 6 that there is a gain in numerical aperture nA—andthus resolution—and on FIG. 7 that there is a gain in depth of field Tcompared with the prior art. The points B in FIGS. 6 and 7 mark thepoint on the curve that can be reached if according to the prior artboth systems were constructed symmetrically with the maximum possiblepencil diameter 32R=32L=stereo basis b=24 mm. Even compared to thistheoretical limiting case an improvement in resolution and depth offield is demonstrated.

FIGS. 6 and 7 correspond to an embodiment in which the entrance pupildiameter of 21 mm on the left side is limited by a lens diameter. Sincethe entrance pupil diameter becomes smaller as magnification reduces,both stereoscopic channels in a wide magnification range of lowmagnifications have the same effective diameter. Therefore, nodifferences in resolution and depth of field arise between both channelsfor such magnifications. Only at high magnifications, in which thediameter of the entrance pupil of the larger channel exceeds thediameter of the limiting lens mentioned of the smaller channel, do theapertures become asymmetric and two different curves develop, whichdemonstrate the advantage of the invention concerning resolution anddepth of field in relation to the prior art.

The angles wR and wL are unequal in the embodiment in FIG. 5. Here theobjective axis 11 and the axis 50 a of the cylinder 50 defining thetelescope (see FIG. 8 b) coincide. The observation angle wR through theright-hand beam path 60R with the higher entrance pupil diameter 31R issmaller than with a symmetrical construction (see FIG. 8 a). As aconsequence of this an object placed centrically to the main objectiveappears as though viewed slightly from the side. In practice this doesnot have a disadvantage of any significance when viewing elongatedobjects.

Data on the two zoom systems can be found in U.S. Pat. No. 6,816,321 B2,(=DE 102 22 041 B4), Table 3. The data is expanded in the table and theoptically effective diameters for the right and left beam paths 60R and60L are listed. Each zoom system consists of four groups of lenses (seeFIGS. 9 and 10), the lens surfaces of which are designated with 101 to105, 106 to 110111 to 115 and 116 to 118. Here the values shown in Table1 below refer to a specific embodiment of the invention.

TABLE 1 Surface Radius Distance ØRight ØLeft number [mm] [mm] n_(d)ν_(d) P_(g, F) P_(C, t) [mm] [mm] 101 102.52 5.07 1.49700 81.6 0.53750.8236 27.0 21.0 102 −42.42 2.0 1.74400 44.8 0.5655 0.7507 26.9 20.9 103−312.91 0.1 26.9 20.9 104 76.50 4.05 1.49 81.6 0.5375 0.8236 26.9 20.9700 105 −102.65 D1 49.35 ÷ 9.02 26.9 20.6 106 −46.18 1.5 1.48749 70.20.5300 0.8924 11.3 11.3 107 20.39 1.96 10.5 10.5 108 −46.61 1.2 1.6204160.3 0.5427 0.8291 10.2 10.2 109 13.60 2.67 1.78470 26.3 0.6135 0.672610.1 10.1 110 40.59 D2 5.26 ÷ 88.89 9.8 9.8 111 44.20 2.35 1.49700 81.60.5375 0.8236 13.0 13.0 112 −58.28 0.1 13.1 13.1 113 32.66 5.13 1.7495035.3 0.5869 0.7140 13.1 13.1 114 15.09 2.99 1.49700 81.6 0.5375 0.823612.1 12.1 115 437.12 D3 50.13 ÷ 6.83 12.0 12.0 116 −29.87 4.95 1.6727032.1 0.5988 0.7046 10.4 10.4 117 −15.67 1.2 1.51633 64.1 0.5353 0.868710.7 10.7 118 43.26 10.7 10.7

From left to right, the lines of Table 1 list the surface number, theradius of curvature, the distance from the next surface, the refractiveindex n_(d), the dispersion v_(d), the partial dispersions P_(g,F) andP_(C,t), and the optically effective diameters of the right and leftbeam path or the first and second telescope systems 3R and 3L. n_(d)denotes the refractive index, v_(d)=(n_(d)−1)/(n_(F)−n_(C)) is the Abbecoefficient, P_(g,F)=(n_(g)−n_(F))/(n_(F)−n_(C)) is the relative partialdispersion for the wavelengths g and F, andP_(C,)t=(n_(C)−n_(t))/(n_(F)−n_(C)) is the relative partial dispersionfor the wavelengths C and t. An air gap is identified by an empty lineor no entry for the material details.

FIG. 8 shows the effect of the positioning of the main objective 2relative to the telescope systems on the two observation angles wL andwR.

FIG. 8 a shows a first setting possibility for the positioning of themain objective 2. Here the two observation directions are arrangedsymmetrically to the optical axis 11 of the objective 2 (wL=wR). Thisposition is referred to below as a “symmetrical arrangement”. This isadvantageous for coaxial illumination of reflecting objects from above.In such an embodiment of the lighting known per se, illumination lightbeneath the tube lenses (41L, 41R in FIG. 5) is conducted into bothstereoscopic channels by means of a beam splitter and directed throughthe channels and the main objective onto the object. Only if wR and wLare symmetrical, can the light directed onto the object by a channel andreflected there be picked up by the other channel and the objectobserved in this way.

FIG. 8 b shows the positioning of the main objective 2 in such a waythat the optical axis of the main objective 2 lies closer to the opticalaxis 33R of the telescope system 3R with the larger entrance pupildiameter. As a consequence of the position of the main objective 2,shown in FIG. 8 b, this possesses an advantageously small objectivediameter. Here the optical axis 11 of the main objective 2 and the axis50 a of the cylinder 50 defining the telescope systems 3R and 3Lcoincide. Here the observation angle wR through the channel 60R with thehigher diameter 32R of the entrance pupil is less than in thesymmetrical structure (see FIG. 8 a). If wR<wL (or, more generally, wRunequal to wL) this embodiment is to be called an “asymmetricalarrangement”. The smaller observation angle and the small diameter ofthe main objective 2 simplify the design of the main objective 2 despitethe unilateral magnification of the numerical aperture. Therefore, theasymmetrical arrangement is particularly preferred.

A main objective with the small diameter in accordance with the“asymmetrical arrangement” can also be used in the “symmetricalarrangement” with coaxial illumination from above. Because the lightfrom the light source, as explained previously, always travels throughboth channels to the observer, the smaller of the two entrance pupildiameters is always effective. It is therefore possible to use in the“symmetrical position” a main objective with the small diameter, whichresults from the “asymmetrical arrangement”, without vignettingoccurring.

FIG. 8 c is the special case in which the optical axis 11 of the mainobjective 2 and the optical axis 33R of the telescope system 3R coincidewith the larger entrance pupil diameter. Here no stereoscopicobservation is provided for. The observation angle is 0°. This settingis particularly advantageous for documentation and measurement tasks athigh resolution. Since here only one stereoscopic channel contributes tothe image, it is likewise possible to use a main objective with thesmall diameter, which results from the “asymmetrical arrangement”.

Similarly, the main objective 2 can be designed to be laterallydisplaceable. Thus variable positioning of the main objective 2 relativeto the magnification changer (or to the first and second telescopesystem 3R and 3L) is achieved. The positions described in FIGS. 8 a to 8c of the main objective 2 can be optionally set. It is mentioned for thesake of completeness that in practice the telescope system with the tubeis advantageously displaced opposite the stationary main objective, inorder to prevent a displacement of the object.

FIGS. 9 and 10 show the beam path of the first telescope system 3R atthe maximum magnification and at the minimum magnification. FIG. 9 showsthe maximum magnification. FIG. 10 shows the minimum magnification. Thefirst and second telescope systems 3R and 3L are built from a first lensgroup 100, a second lens group 200, a third lens group 300 and a fourthlens group 400 (see Table 1 above). D1, D2 and D3 denote the variabledistances between the lens groups 100, 200, 300 and 400. Between thefirst lens group 100 and the second lens group 200 at maximummagnification the distance D1=49.35 mm. Between the second lens group200 and the third lens group 300 at maximum magnification the distanceD2=5.26 mm. Between the third lens group 300 and the fourth lens group400 at maximum magnification the distance D3=50.13 mm. At minimummagnification the composition of the distances is different. Between thefirst lens group 100 and the second lens group 200 at minimummagnification the distance D1 is 9.02 mm. Between the second lens group200 and the third lens group 300 at minimum magnification the distanceD2 is 88.89 mm. Between the third lens group 300 and the fourth lensgroup 400 at minimum magnification the distance D3 is 6.83 mm. Table 1shows the radii of the surface numbers in the groups of lenses, asillustrated in FIG. 9 and FIG. 10. The table also shows that theobjective-side diameters φ of the refracting elements of the firsttelescope system 3R are greater than the diameters φ of the refractingelements of the second telescope system 3L. The edge beams which definethe diameter of the entrance pupil are illustrated as an unbroken lineand the main beam for the maximum field angle as a broken line. See inthis respect as well as with regard to the individual elements withtheir reference symbols the description of FIGS. 1 a and 1 b of DE 10222 041 B4 already mentioned.

It is recognized in FIG. 10 that the main beam has a considerabledistance to the outside diameter of the group 100, while in FIG. 9 theedge beams in the case of the same group 100 run close to the outsidediameter. It is thus obvious that in the left telescope 3L of the leftchannel the diameter of the group 100 can be reduced without the mainbeam being blocked as a result. This is the one necessary condition forstereoscopic viewing to be possible up to the image edge. This conditionthat the main beam to the image edge must not be blocked in the channelwith the smaller diameter, is simultaneously a criterion for the designof an afocal zoom system suitable for a stereomicroscope of unequaloptically effective channel diameters. This condition is thus a guidefor positioning of the entrance pupil with low magnifications.

1. A telescopic stereomicroscope comprising: a first beam path; a secondbeam path; a first telescope system being disposed in the first beampath having a first optical element and a first magnification, a secondtelescope system disposed in the second beam path and having a secondoptical element corresponding to the first optical element and a secondmagnification, wherein the first and second magnifications are equal andare adjustable synchronously to each other, and wherein the firstoptical element has a different optically effective diameter than thecorresponding second optical element; and a common main objectiveallocated to both the first and second beam paths, wherein the firsttelescope system has a first diaphragm and the second telescope systemhas a second diaphragm, the first diaphragm being variable independentlyof the second diaphragm.
 2. A telescopic stereomicroscope comprising: afirst beam path; a second beam path; a first telescope system beingdisposed in the first beam path having a first optical element and afirst magnification; a second telescope system disposed in the secondbeam path and having a second optical element corresponding to the firstoptical element and a second magnification, wherein the first and secondmagnifications are equal and are adjustable synchronously to each other,and wherein the first optical element has a different opticallyeffective diameter than the corresponding second optical element; and acommon main objective allocated to both the first and second beam paths,wherein the first telescope system has a first diaphragm having a firstdiaphragm opening and the second telescope system has a second diaphragmhaving a second diaphragm opening, wherein the first and seconddiaphragms are operable such that, in a first setting, a ratio of thefirst and second diaphragm openings is adjustable, and, in a secondsetting, wherein the first and second diaphragm openings aresimultaneously variable such that the ratio of the diaphragm openings isunchanged.
 3. A telescopic stereomicroscope comprising: a first beampath, a second beam path; a first telescope system being disposed in thefirst beam path having a first optical element and a firstmagnification; a second telescope system disposed in the second beampath and having a second optical element corresponding to the firstoptical element and a second magnification, wherein the first and secondmagnifications are equal and are adjustable synchronously to each other,and wherein the first optical element has a different opticallyeffective diameter than the corresponding second optical element; acommon main objective allocated to both the first and second beam paths;and a filter configured to be introduced into and removed from one ofthe first and second beam paths in a direction perpendicular to therespective beam path of the telescope system having a larger opticallyeffective diameter or a larger entrance pupil diameter.
 4. Thetelescopic stereomicroscope as recited in claim 3, wherein the filter isa brightness correction filter.
 5. The telescopic stereomicroscope asrecited in claim 3, wherein the filter is configured to be manuallyoperated.
 6. The telescopic stereomicroscope as recited in claim 3,wherein the filter is configured to be operated automatically byoperation of a magnification selection.